Phagocytosis and intracellular killing of bacteria by polymorphonuclear leukocytes is classically associated with an augmented oxygen consumption, and with increased activity of the hexose monophosphate shunt, and the enzymes involved in oxidation of reduced pyridine nucleotides and reduced glutathione. As we have found that phagocytosis of virulent S. typhis is not associated with the increased consumption, we believe that virulence may be associated with an inhibition of normal polymorphonuclear leukocyte function. We proposed to study the intraleukocytic metabolic effects of the ingestion of S. typhi to determine those bacterial virulence factors which may inhibit normal leukocyte bacteriocidal function. We believe that these results will provide insight into the mechanism by which certain bacteria are established as intracellular parasites.